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<FONT color="green">001</FONT>    package org.hackystat.utilities.time.period;<a name="line.1"></a>
<FONT color="green">002</FONT>    <a name="line.2"></a>
<FONT color="green">003</FONT>    import java.util.Calendar;<a name="line.3"></a>
<FONT color="green">004</FONT>    import java.util.Date;<a name="line.4"></a>
<FONT color="green">005</FONT>    import java.util.Locale;<a name="line.5"></a>
<FONT color="green">006</FONT>    import java.util.TimeZone;<a name="line.6"></a>
<FONT color="green">007</FONT>    <a name="line.7"></a>
<FONT color="green">008</FONT>    /**<a name="line.8"></a>
<FONT color="green">009</FONT>     * Provides a cache mechanism for obtaining a single "canonical" Day instance associated with any<a name="line.9"></a>
<FONT color="green">010</FONT>     * given UTC time stamp.  "Canonical" means that for any UTC value within a given day, the<a name="line.10"></a>
<FONT color="green">011</FONT>     * same Day instance will be returned.  Performance monitoring has indicated that certain types of<a name="line.11"></a>
<FONT color="green">012</FONT>     * analyses spend significant resources producing and discarding Day instances.  This class is<a name="line.12"></a>
<FONT color="green">013</FONT>     * designed to lower the overhead of such computations by maintaining a cache of Day instances<a name="line.13"></a>
<FONT color="green">014</FONT>     * that can be shared.  Note that the DayCache cannot be used in situations where the original UTC<a name="line.14"></a>
<FONT color="green">015</FONT>     * value is needed later, since the Day instance that is returned will not return the original UTC<a name="line.15"></a>
<FONT color="green">016</FONT>     * value through invocation of the getTime() method.<a name="line.16"></a>
<FONT color="green">017</FONT>     * &lt;P&gt;<a name="line.17"></a>
<FONT color="green">018</FONT>     * This class is a "helper" class to Day. It is used only within the constructors for Day. There<a name="line.18"></a>
<FONT color="green">019</FONT>     * are no other clients to this class. Normal users should manipulate Day instances by calling the<a name="line.19"></a>
<FONT color="green">020</FONT>     * associated Day.getInstance() methods.<a name="line.20"></a>
<FONT color="green">021</FONT>     * &lt;p&gt;<a name="line.21"></a>
<FONT color="green">022</FONT>     * DayCache implements a sliding "window" cache of 730 instances corresponding to 730 days.  The<a name="line.22"></a>
<FONT color="green">023</FONT>     * middle instance corresponds to the day that this cache was first used (which normally<a name="line.23"></a>
<FONT color="green">024</FONT>     * corresponds to the server startup day.  If the DayCache is asked for a Day instance outside<a name="line.24"></a>
<FONT color="green">025</FONT>     * this window, then a  non-cached, regular Day instance is returned. The reason for this design<a name="line.25"></a>
<FONT color="green">026</FONT>     * is to minimize object creation: we can do arithmetic to get the array index corresponding to a<a name="line.26"></a>
<FONT color="green">027</FONT>     * UTC value.<a name="line.27"></a>
<FONT color="green">028</FONT>     * &lt;p&gt;<a name="line.28"></a>
<FONT color="green">029</FONT>     * Use only Day.equals() to compare two Day instances. Do not use '=='.<a name="line.29"></a>
<FONT color="green">030</FONT>     * <a name="line.30"></a>
<FONT color="green">031</FONT>     * The Calendar is forced to Locale.US to ensure constant week boundaries. <a name="line.31"></a>
<FONT color="green">032</FONT>     * <a name="line.32"></a>
<FONT color="green">033</FONT>     * @author Philip M. Johnson<a name="line.33"></a>
<FONT color="green">034</FONT>     * @version $Id: DayCache.java,v 1.1.1.1 2005/10/20 23:56:44 johnson Exp $<a name="line.34"></a>
<FONT color="green">035</FONT>     */<a name="line.35"></a>
<FONT color="green">036</FONT>    public class DayCache {<a name="line.36"></a>
<FONT color="green">037</FONT>      /** The singleton DayCache instance. */<a name="line.37"></a>
<FONT color="green">038</FONT>      private static DayCache theCache = new DayCache();<a name="line.38"></a>
<FONT color="green">039</FONT>    <a name="line.39"></a>
<FONT color="green">040</FONT>      /** Number of milliseconds in a day. */<a name="line.40"></a>
<FONT color="green">041</FONT>      private long millisInDay = 1000 * 60 * 60 * 24;<a name="line.41"></a>
<FONT color="green">042</FONT>    <a name="line.42"></a>
<FONT color="green">043</FONT>      /** The first UTC time that will be stored in the cache, initialized in the constructor. */<a name="line.43"></a>
<FONT color="green">044</FONT>      private long minUTC = 0;<a name="line.44"></a>
<FONT color="green">045</FONT>    <a name="line.45"></a>
<FONT color="green">046</FONT>      /** The last UTC time that will be stored in the cache, initialized in the constructor. */<a name="line.46"></a>
<FONT color="green">047</FONT>      private long maxUTC = 0;<a name="line.47"></a>
<FONT color="green">048</FONT>    <a name="line.48"></a>
<FONT color="green">049</FONT>      /** The array of cached Day instances. day[365] is the day the server started. */<a name="line.49"></a>
<FONT color="green">050</FONT>      private Day[] days = new Day[730];<a name="line.50"></a>
<FONT color="green">051</FONT>      <a name="line.51"></a>
<FONT color="green">052</FONT>      /** The date the DayCache was constructed. */<a name="line.52"></a>
<FONT color="green">053</FONT>      private Date startupDate;<a name="line.53"></a>
<FONT color="green">054</FONT>    <a name="line.54"></a>
<FONT color="green">055</FONT>      /**<a name="line.55"></a>
<FONT color="green">056</FONT>       * The singleton DayCache instance that provides access to a "window" of cached,  canonical Day<a name="line.56"></a>
<FONT color="green">057</FONT>       * instances.  The cache is lazily instantiated.<a name="line.57"></a>
<FONT color="green">058</FONT>       */<a name="line.58"></a>
<FONT color="green">059</FONT>      private DayCache() {<a name="line.59"></a>
<FONT color="green">060</FONT>        Calendar cal = Calendar.getInstance(Locale.US);<a name="line.60"></a>
<FONT color="green">061</FONT>        cal.set(Calendar.HOUR_OF_DAY, 0);<a name="line.61"></a>
<FONT color="green">062</FONT>        cal.set(Calendar.MINUTE, 0);<a name="line.62"></a>
<FONT color="green">063</FONT>        cal.set(Calendar.SECOND, 0);<a name="line.63"></a>
<FONT color="green">064</FONT>        cal.set(Calendar.MILLISECOND, 0);<a name="line.64"></a>
<FONT color="green">065</FONT>        // I use 364 to avoid off by one errors at expense of thinking hard. :-)<a name="line.65"></a>
<FONT color="green">066</FONT>        this.minUTC = cal.getTimeInMillis() - (364 * millisInDay);<a name="line.66"></a>
<FONT color="green">067</FONT>        this.maxUTC = cal.getTimeInMillis() + (364 * millisInDay);<a name="line.67"></a>
<FONT color="green">068</FONT>        <a name="line.68"></a>
<FONT color="green">069</FONT>        this.startupDate = new Date();<a name="line.69"></a>
<FONT color="green">070</FONT>      }<a name="line.70"></a>
<FONT color="green">071</FONT>    <a name="line.71"></a>
<FONT color="green">072</FONT>      /**<a name="line.72"></a>
<FONT color="green">073</FONT>       * Returns the singleton DayCache.<a name="line.73"></a>
<FONT color="green">074</FONT>       * <a name="line.74"></a>
<FONT color="green">075</FONT>       * &lt;p&gt;<a name="line.75"></a>
<FONT color="green">076</FONT>       * To be used only by the Day class constructors.<a name="line.76"></a>
<FONT color="green">077</FONT>       * &lt;/p&gt;<a name="line.77"></a>
<FONT color="green">078</FONT>       *<a name="line.78"></a>
<FONT color="green">079</FONT>       * @return The DayCache.<a name="line.79"></a>
<FONT color="green">080</FONT>       */<a name="line.80"></a>
<FONT color="green">081</FONT>      static DayCache getInstance() {<a name="line.81"></a>
<FONT color="green">082</FONT>        return theCache;<a name="line.82"></a>
<FONT color="green">083</FONT>      }<a name="line.83"></a>
<FONT color="green">084</FONT>    <a name="line.84"></a>
<FONT color="green">085</FONT>      /**<a name="line.85"></a>
<FONT color="green">086</FONT>       * Return the cached Day instance corresponding to timestamp if plus/minus 364 days from the day<a name="line.86"></a>
<FONT color="green">087</FONT>       * the Cache was initialized.  Otherwise, returns a new Day instance.  Note that cached Day<a name="line.87"></a>
<FONT color="green">088</FONT>       * instances will usually have an internal UTC value that is different  from timestamp.<a name="line.88"></a>
<FONT color="green">089</FONT>       * <a name="line.89"></a>
<FONT color="green">090</FONT>       * &lt;p&gt;<a name="line.90"></a>
<FONT color="green">091</FONT>       * To be used only by the Day class constructors.<a name="line.91"></a>
<FONT color="green">092</FONT>       * &lt;/p&gt;<a name="line.92"></a>
<FONT color="green">093</FONT>       *<a name="line.93"></a>
<FONT color="green">094</FONT>       * @param timestamp The UTC value falling within the Day of interest.<a name="line.94"></a>
<FONT color="green">095</FONT>       *<a name="line.95"></a>
<FONT color="green">096</FONT>       * @return The cached Day, or a new Day if it returns outside the cache.<a name="line.96"></a>
<FONT color="green">097</FONT>       */<a name="line.97"></a>
<FONT color="green">098</FONT>      Day getDay(long timestamp) {<a name="line.98"></a>
<FONT color="green">099</FONT>        if ((timestamp &gt;= maxUTC) || (timestamp &lt;= minUTC)) {<a name="line.99"></a>
<FONT color="green">100</FONT>          return new Day(timestamp);<a name="line.100"></a>
<FONT color="green">101</FONT>        }<a name="line.101"></a>
<FONT color="green">102</FONT>        else {<a name="line.102"></a>
<FONT color="green">103</FONT>          // the dstSavings value is used to correct the timestamps that have added the Daylight<a name="line.103"></a>
<FONT color="green">104</FONT>          // Savings Time to the UTC. the DST is usually configured in the OS by the user. <a name="line.104"></a>
<FONT color="green">105</FONT>          // if the system clock isn't DST enabled, dstSavings will be zero.<a name="line.105"></a>
<FONT color="green">106</FONT>          int dstSavings = 0;<a name="line.106"></a>
<FONT color="green">107</FONT>          if (TimeZone.getDefault().inDaylightTime(this.startupDate) &amp;&amp; <a name="line.107"></a>
<FONT color="green">108</FONT>              !TimeZone.getDefault().inDaylightTime(new Date(timestamp))) {<a name="line.108"></a>
<FONT color="green">109</FONT>            dstSavings = -TimeZone.getDefault().getDSTSavings();<a name="line.109"></a>
<FONT color="green">110</FONT>          }<a name="line.110"></a>
<FONT color="green">111</FONT>          else if (!TimeZone.getDefault().inDaylightTime(this.startupDate) &amp;&amp; <a name="line.111"></a>
<FONT color="green">112</FONT>              TimeZone.getDefault().inDaylightTime(new Date(timestamp))) {<a name="line.112"></a>
<FONT color="green">113</FONT>            dstSavings = TimeZone.getDefault().getDSTSavings();<a name="line.113"></a>
<FONT color="green">114</FONT>          }<a name="line.114"></a>
<FONT color="green">115</FONT>          int index = (int) (((timestamp + dstSavings) - minUTC ) / millisInDay);<a name="line.115"></a>
<FONT color="green">116</FONT>          if (days[index] == null) {<a name="line.116"></a>
<FONT color="green">117</FONT>            days[index] = new Day(timestamp);<a name="line.117"></a>
<FONT color="green">118</FONT>          }<a name="line.118"></a>
<FONT color="green">119</FONT>    <a name="line.119"></a>
<FONT color="green">120</FONT>          return days[index];<a name="line.120"></a>
<FONT color="green">121</FONT>        }<a name="line.121"></a>
<FONT color="green">122</FONT>      }<a name="line.122"></a>
<FONT color="green">123</FONT>    }<a name="line.123"></a>




























































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